Transport distraction osteogenesis (TDO) was pioneered at the turn of the 20th century. It was originally applied as a method of leg lengthening to correct discrepancies between legs. As such, its early development was in the area of orthopaedics. The concepts have since been adapted to maxillofacial reconstructive surgery. Transport distraction osteogenesis is now commonly applied to regeneration of the maxilla and mandible where they are absent as well as the correction of various facial bone abnormalities.
Transport distraction osteogenesis involves surgical fracture of the bone, a latent period to facilitate initial healing of the fracture, and then incremental, relative distraction of the fracture surfaces. The relative displacement of the fracture surfaces facilitates the generation of new bone at the interface. By incrementally distracting the healing fracture surfaces at a rate of approximately 1 mm per day, it is possible to gradually extend existing bone segments or generate sections of entirely new bone where deficiencies are present.
During Transport Distraction Osteogenesis, distraction is mechanically controlled and, as such, the mechanical stability and control of the healing environment is crucial to the resultant physical properties of the generated bone and thus the success of the procedure.
The most common abnormalities of the maxillofacial region are congenital defects, bone disease or the result of surgical removal of tumours. The effects of these disorders include total discontinuity of the maxilla or mandible, and the total or partial absence of the alveolar ridge. Such defects have serious implications for the quality of life of patients after reconstructive surgery as the maxilla and mandible are responsible for the crucial functions of chewing, swallowing, speaking and facial expression.
Transport distraction osteogenesis offers numerous benefits over other facial reconstruction techniques such as bone grafting. The benefits of transport distraction osteogenesis include reduced patient trauma and faster patient recovery. It also eliminates the associated risks of bone grafting such as rejection of the graft/implant by the human body. The major benefit, however, is that transport distraction osteogenesis regenerates not only the structural bone, but also the surrounding soft tissue and blood supply. In the case of grafting, a prolonged period of healing is required before these are restored.
Reconstruction of large maxillectomy defects following tumour resection presents a formidable challenge to both surgeons and prosthodontists. In addition to the hermetic obturation of the large oro-nasal-antral defects, successful rehabilitation has to take into account the demands of aesthetics, function, deglutition and speech. To this end, it would be desirable to re-create a functional palatal vault, alveolar ridge that can house dental-implants and a vestibule for supportive form and function of cheeks. Due to the large size and complexity of various maxillectomy defects, the structural and functional restoration requires composite tissue replacement involving free vascularized flaps harvested from the tibia or fibula. These procedures demand long and skillful surgical techniques and, though often highly successful, are not always predictable and cause significant donor site morbidity.
Various transport distractors have been developed by companies such as KLS Martin and BIOMET Microfixation. However, most existing maxillofacial transport distractors are not practically suited to distraction in the anterior curved segment of the maxilla. These devices are uncomfortably large and do not perform well on curvilinear trajectories.
Titanium fixation plating systems are widely used in maxillo-facial reconstruction. They are used to create a structural connection between bone anatomies that require support. In addition, titanium plating systems can be used to form a rigid rail for guiding distraction, hereinafter referred to as the ‘trajectory rail’, for transport distractors.
Some distractors are capable of following curvilinear trajectories, but the nature of the designs makes them inappropriate for distraction along curves such as those present in the anterior segments of the mandible and maxilla. This problem has been partially resolved by approximating the desired curve with multiple linear distractions or the use of multiple distractors simultaneously. This is known as bifocal distraction. However, it has been found that a two-stage mandibular distraction requires four invasive operations whilst the generated geometry is not true to the ideal form of the mandible.
Due to the complex anatomical constraints of the maxilla, currently available distractors cannot deal with the demands of the upper jaw and at present there are no transport distractors available for anterior to posterior distraction in the maxilla.
United States published patent application US20100152734 describes a proposed device in which a carriage that can be secured to one part of the maxilla or mandible, as the case may be, and a track having a series of transverse grooves therein that cooperate with a worm gear to move the carriage along the track incrementally as required in a transport distraction osteogenesis procedure. However, the device proposed is rather thick in that it requires appreciable space in the direction at right angles to the maxilla or mandible thereby contributing significantly to patient discomfort by protruding and becoming obtrusive inside the patient's mouth. The device described also has a carriage that is detachable from bracket flanges thereby complicating the mechanism further and making it more bulky. The driver of the worm gear and the position of the worm gear allow the device to be accessed only as long as there is available space in the patient's mouth and as long the device is placed on the mandible. Considering the anatomical variations and inaccessible spaces of the maxilla, this device besides being cumbersome, is inappropriate to provide traction, especially as the demands may dictate, such as from the right side through the front to the left and to the back of the maxilla. Also in the maxilla, a three dimensional curvilinear traction may be necessary and the device described may not be able to provide locomotion on a spiral.